GB553091A - Piezoelectric oscillators - Google Patents

Abstract

553,091. Valve-generating circuits. STANDARD TELEPHONES & CABLES, Ltd. April 2, 1942, No. 4405. Convention date, April 2, 1941. [Class 40 (v)] A piezo-electric controlled oscillator comprises an electron discharge device having input and output circuits, a piezo-electric element connected to the electron discharge device and means mechanically associated with both circuits for simultaneously varying their tuning in the same direction whereby a particular resonance frequency of the piezo-electric element may be selected for the oscillator. As shown the valve 10 has connected in its anode circuit a tuned circuit 18, 33 while between grid and cathode are connected a piezo-electric crystal arrangement 19 in series with a tuned circuit 30, 32 having a trimmer 34. Condenser 18 is adjustable to tune the anode circuit to any one of the several series of harmonic frequencies at which the crystal arrangement 19 can oscillate. In order that at each of the selected frequencies, the grid input reactance is positive, condenser 30 is equal to condenser 18 and is gang tuned with it while inductance 32 is made less than inductance 33. Thus circuit 30, 32 is always tuned to a higher frequency than that selected and so presents a positive reactance. The output is taken from terminals 27. The piezo-electric crystal arrangement 19 comprises two sets of quartz plates 44-46 and 48-50 each plate having a different fundamental frequency the complete assembly being thus able to generate six series of harmonic frequencies. A central terminal plate 42 is in contact with electrode plates 37, 39 against which the two sets of crystal plates are pressed by means of outer electrodes 36, 39 and springs 43, 47 which bear against outer terminal plates 40, 41 mounted on the inside of an insulating container. A switch 51 enables either of the sets of plates to be selected. although the two sets may be strapped for use in parallel.